The current square is the result of heavy restoration carried out at the end of the 800s by the architect Giuseppe Partini, that altered its general image, building on and adding new structures, in the neo-gothic style of the time.
At the back of the square, essentially extracted from the garden of the adjacent Palazzo Spannocchi, the ninth century façade (by Partini) of the Salimberi Fortress stands out. It is one of the most imposing, complex and strengthened fortresses of medieval Siena, and the home of the great Salimbeni family until they were hunted from Siena and their possessions confiscated (in 1419).
The fortress then passed to the Council and finally, in 1866, it was sold to Monte dei Paschi, of whom it is said, decided to restore it. At the centre of the square is the monument to Sallustio Bandini, the work of Tito Sarrochi, in 1880. Today the whole square, reorganised by a recent restoration (1963-72), houses various buildings from the thirteenth century: towers, a fortress, the Fondaco of the Salimbeni, and the small palace of Ranieri Salimbeni.
The fortress hosts a notable collection of works of art, that is widening thanks to the same Monte dei Paschi: amongst others, there are masterpieces by Sassetta, Pietro Lorenzetti and Beccafumi. In addition to the Archivio Storico, the collection is a precious witness to the economic history of Siena.